1. Field of the Invention
The present invention relates to a method of, and an apparatus for, detecting radial tilt of a disc.
2. Description of the Related Art
Tilt, which is a reference value representing tilt of a disc, is classified into a radial tilt and a tangential tilt. The radial tilt represents a tilt of the disc in a radial direction thereof, and the tangential tilt represents a tilt of the disc in a circumferential direction thereof. The tilt can be measured from an angle between an incident direction and a reflected direction of a laser beam which is perpendicularly incident on a disc surface. Thus, the tilt is expressed by an angle. In the case of DVDs, the radial tilt should be 0.8 degree or less, and the tangential tilt should be 0.3 degree or less.
A disc drive has a control system which moves a laser beam spot to a target track by maintaining the laser beam on a recording surface of the disc, a control system which moves a laser beam spot to follow a target track by maintaining the laser beam on a recording surface of the disc, and a control system which rotates the disc. The control systems are called a focusing and seek servo control system, a tracking servo control system, and a rotating servo control system, respectively.
The accurate detection of the radial tilt of the disc is important to the operation of these servo control system, since precise servo control may be performed when the radial tilt is accurately detected resulting in smooth reproducing and recording of the disc.